The present invention pertains to a multilayer film and a method of manufacture therefor. Specifically, the multilayer film of the present invention features a polyolefin based material which closely replicates the mechanical properties normally associated with a film of plasticized polyvinylchloride (PVC). This material is particularly suitable for use as a substrate for bandages and surgical dressings, but the film of the present invention is not limited to only medical applications and could be used as a substitute material in other PVC based articles.
Solution cast, plasticized polyvinylchloride (PVC) films are frequently used as substrates for bandages and similar disposable articles. Plasticized PVC films are used in these applications primarily because they offer a particular set of mechanical properties. Plasticized PVC films possess desirable properties including easy stretch, high degree of recovery, low fatigue and minimal permanent set. However, plasticized PVC film has become less desirable because of known or suspected carcinogens associated with both the PVC monomer and the various plasticizers used in its production. Obviously, given the widespread use of these films in bandages and other medical applications where the polymer substrate may come into direct contact with open skin, blood, and other bodily fluids, it would be highly desirable to produce a new polymeric film which behaves mechanically like a plasticized PVC film, but is formed of materials that are free of suspected or known carcinogenic components.
Such a substitute or replacement film for plasticized PVC film has been desired for some time. One category of polymer films, polyolefins, are quite common and are used in a wide variety of applications. However, polyolefins in general do not recover from stretching as well as plasticized PVC films do. Ideally, a PVC replacement film will stretch easily, but recover completely. An ideal film would not fatigue or retain a permanent set. Additionally, if a substitute material could also provide improved breathability (i.e. higher MVTR) as compared to plasticized PVC film, this would also be a plus.
In short, there is a need for polymeric films which can replace plasticized PVC films in a variety of medical and non-medical applications. Specifically, there is a need for polyolefin based materials which have similar hysteresis (stress/strain) characteristics to plasticized PVC film as well as having a similar folding and conforming nature to plasticized PVC films.
The present invention discloses a coextruded multilayer film particularly adapted for use as a replacement film for plasticized PVC in a variety of medical and non-medical applications. It has been discovered that polyolefin based formulations exist that closely match the mechanical performance criteria of a control plasticized PVC material. These polyolefin based formulations do not contain any known or suspected carcinogenic compounds and may be produced at costs that are highly competitive with the costs associated with a conventional plasticized PVC film.
In one preferred embodiment, the multilayer film of the present invention comprises a core layer which is coextruded and disposed between two outer skin layers. The core layer is generally about 65% to about 95% of the multilayer film thickness, and the two exterior skin layers are each about 2.5% to about 17.5% of the multilayer film thickness. One preferred material for the core layer is a blend of metallocene ultra low density polyethylene (ULDPE) polyolefin plastomer and an ethylene methyl acrylate (EMA) copolymer. Each coextruded skin layer may be made of another polyolefin blend such as linear low density polyethylene (LLDPE) and low density polyethylene (LDPE).